1. Field of the Invention
This invention relates to methods of assaying pyrrole-containing biological compounds and chemical compositions that can be used in such methods. More specifically, it relates to a method for detecting pyrrole-containing molecules that are markets of particular disease states.
2. Description of Related Art
Erlich's reagent, or p-dimethylaminobenzaldehyde (1), is a molecule that can react with pyrroles and indoles to form a chromogenic compound.

See G. Lombard and V. Dowell, J. Clin. Microbiol.
(1983) 18:609–613. The mechanism of action is typically described as an electrophilic attack on the α-carbon atom of a pyrrole. This attack forms a highly conjugated cation that absorbs light in the visible spectrum. Such a mechanism is graphically represented in Scheme A above.
The reaction of Ehrlich's reagent with certain compounds has been discussed. For instance, Iyer reported a pyrrole is formed when LGE2 is reacted with proteins. See Iyer et al., J. Org. Chem. (1994) 59:6038–6043. When the pyrrole was contacted with Ehrlich's reagent in the presence of BF3.OEt2, a blue-green chromophore was produced. The chromophore was identified as a pyrrolic electrophilic substitution product.
Lombard reported the reaction between Ehrlich's reagent and bacterially derived indoles. See G. Lombard and V. Dowell, J. Clin. Microbiol. (1983) 18:609–613. The sensitivity of the reagent was compared to two other indole detecting compounds: Kovac's reagent and DMCA. Ehrlich's reagent was reported to be 10 times less sensitive than DMCA and 10 times more sensitive than Kovac's reagent in detecting indole.
While Ehrlich's reagent has been used to roughly detect the presence of pyrroles or indoles in a targeted material, improved compositions and methods for detecting such heterocycles are desirable, especially methods that provide for detecting pyrrole-containing molecules that are markers of particular disease states.